1. Technical Field
The disclosed embodiments relate to a digital-to-analog converter, and more particularly to a digital-to-analog converter with power on/off transient suppression.
2. Description of the Related Art
Currently, digital-to-analog converters (DACs) are widely used in audio and video applications, which are devices for converting a digital (usually binary) code to at least an analog signal. In audio applications, the DAC may have a single-end output or differential outputs for driving a load, such as a headphone or a speaker, according to design consideration for various products.
In single-end output DACs, a direct current (DC) blocking capacitor may be employed between an amplifier of the DAC and a load in order to block the DC voltage. However, the single-end DAC may suffer from large transient signals appearing at the outputs when initially powered on. Such DACs present an analog output centered on a signal ground level, such as ½ VDD. The transient signal occurs when a power is applied to the DAC, and the analog outputs are required to move from a ground (GND) level to the signal ground level. If the transient signal occurs rapidly, it can be approximated as a step function, which has energy at all frequencies. On power-up, such a system can suffer an annoying noise, such as a “pop” or “click”, heard by a speaker when the DAC initially charges the blocking capacitor to the signal ground level.
Similarly, a click or pop may occur when the system is powered off. On entering the power-off state, the charge on the blocking capacitor remains. When the power is removed, the residual charge of the blocking capacitor may discharge rapidly across the load resulting in a loud noise.